Apparatus and method for use in thermoelectric power generation

ABSTRACT

An apparatus and method for generating thermoelectric power utilizes a hollow shell member having a cavity defined therein and a cartridge member disposed within the cavity, wherein the cartridge member has a combustion chamber defined therein. The cartridge member is mounted such that a space exists between the interior surface of the shell member and the exterior surface of the cartridge member. Thermoelectric elements are mounted to the exterior surface of the shell member such that no air spaces exist therebetween. A mixture of a combustible fuel and air is introduced into the chamber, the air/fuel ratio being less than the stoichiometric ratio for methane. Heat generated within the combustion chamber upon combustion of the fuel is transferred via the shell member to the thermoelectric elements which generate electrical energy in response thereto.

This is a divisional of application Ser. No. 699,287, filed Feb. 7,1985.

BACKGROUND OF THE INVENTION

This invention relates to an apparatus for use in thermoelectric powergeneration. In another aspect, the invention relates to a method ofthermoelectric power generation.

A thermoelectric generator is essentially a device wherein heat isconverted directly to electrical energy. The components of athermoelectric generator include a heat source and thermoelectricelements for receiving heat from the heat source and converting suchheat to electrical energy. A thermoelectric generator also typicallyincludes some external electronic circuitry such as a DC-DC conversioncircuit for receiving power from the thermoelectric elements at a lowvoltage, and delivering current at a higher voltage. Thermoelectricgenerators are usually operable in all weather conditions, and can beleft unattended for long periods of time. Therefore, such generators areparticularly suitable for use in remote regions where normal sources ofelectric power are not available.

Several types of heat sources are used in thermoelectric generators,including sources based on nuclear and solar energy. One of the mostcommon types of thermoelectric generators is the fossil fuel generator,wherein combustion of a fossil fuel such as natural gas takes place.

Heretofore, such fossil fuel generators have had several seriouslimitations. One such limitation involves ineffective use of sour gas,(gas having high concentrations of hydrogen sulfide) particularly infossil fuel generators of the type wherein fuel is combusted in thepresence of a catalyst. After operation for a period of time on sourgas, elemental sulfur is produced which plates the catalyst, therebyrendering the catalyst ineffective. Another limitation involves theability to use fuels having different heating values. In prior fossilfuel generators, changing from one fuel with a certain heating value toanother fuel with a different heating value requires an adjustment ofthe air/fuel flow ratio. Such an adjustment can be time consuming andinconvenient.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide anapparatus and method for use in thermoelectric power generation.

Another object of the present invention is to provide an apparatus andmethod for use in thermoelectric power generation wherein fuel gaseshaving high concentrations of hydrogen sulfide can be used effectively.

It is yet another object of the invention to provide a method ofgenerating power thermoelectrically wherein fuels having differentheating values can be used conveniently such that no adjustments arerequired when changing from one fuel to another fuel.

Certain of the above objects are realized in an apparatus which includesa hollow shell member and a hollow cartridge member disposed within theshell member. The cartridge member has an interior surface which definesthe chamber, and an exterior surface, a portion of which is in contactwith the interior surface of the shell member such that a space existsbetween the surfaces. At least one thermoelectric element is mounted tothe shell member so as to be in direct thermal contact therewith. Thethermoelectric element is mounted such that substantially no air spacesexist between the shell member exterior surface and the thermoelectricelement.

According to another aspect of the present invention, there is provideda shell member and cartridge member substantially as described above.Heat is generated within the chamber, such heat being provided to atleast one thermoelectric element in direct thermal contact with theexterior surface of the shell member.

According to further aspects of the invention, an apparatus and methodare provided in which a combustible fuel and air are mixed to form amixture, the air/fuel ratio being less than the stoichiometric ratio formethane. The mixture is passed into a combustion chamber where the fuelis combusted so as to generate heat. In thermoelectric power generation,this heat may be provided to thermoelectric elements which generateelectrical energy.

According to a preferred embodiment described hereinafter, a catalyst iscontained in the above described chamber, through which is flowed amixture of a fuel gas and air. Catalytic oxidation of the fuel gas takesplace in the chamber. By mounting the cartridge within the shell asdescribed above, temperatures in the combustion chamber can bemaintained at a sufficiently high level to oxidize the sulfur in a fuelhaving hydrogen sulfide therein. Consequently, production of elementalsulfur, which will plate the catalyst, is avoided. Furthermore, byintroducing into the combustion chamber a fuel rich mixture having anair/fuel ratio less than the stoichiometric ratio for methane, fuels ofdifferent heating values can be used without adjustments.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, brieflydescribed below.

FIG. 1 is a view of a thermoelectric generator designed according to theinvention, which includes a burner unit, as it is mounted in a case.

FIG. 2 is a cross sectional view of the burner unit shown in FIG. 1.

FIG. 3 is an end view of the burner unit which shows thermoelectricelements mounted between the burner unit and the case.

FIG. 4 is a graphical plot of various parameter versus time according toa particular example wherein methane was employed in a thermoelectricgenerator designed according to the invention.

FIG. 5 is a graph of output in watts versus time for a thermoelectricgenerator designed according to the invention employing fuel with a highconcentration of hydrogen sulfide.

FIG. 6 is a graph of various parameters versus time for a thermoelectricgenerator designed according to the invention initially running onmethane, wherein propane is introduced in gradually increasing amounts.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1, the apparatus shown includes a case section 10within which are mounted various components of a thermoelectricgenerator according to the present invention. The thermoelectricgenerator serves as a power source in a comuterized flow measurementunit, the remainder of which is mounted within another case section. Theportion of the unit being so powered by the generator forms no part ofthe present invention and is therefore not shown. A burner unit 12,hereinafter described in detail with reference to FIGS. 2 and 3, ismounted to the wall of case 10 by means of suitable mounting posts. Twothermoelectric modules, shown in dashed form at 14 and 16, arepositioned between burner unit 12 and case 10 so as to be in directthermal contact with burner unit 12. Since dimensions of variousmounting structures, etc. may vary relative to one another in responseto the relatively high temperatures achieved in proximity to burner unit12, it is preferable that burner unit 12 be held in place by means of aspring relief mounting, details of which are not shown, which permitsvariations in appropriate dimensions without any significant change inspring forces. This sort of design prevents buildup of excessivecompressive stresses on the thermoelectric modules 14 and 16. Modules 14and 16 are of conventional design, and as is well known to those skilledin the art generate electrical energy in response to a temperaturegradient across the modules.

Thermoelectric modules as used in the illustrated embodiment are widelycommercially available, and generally comprise a plurality ofthermoelectric elements sandwiched between two insulating plates madeof, for example, a ceramic material. One commercially available moduleparticularly suitable for use with the present invention is the type2004 module manufactured by the Cambion Corporation of Cambridge, Mass.In addition, although two modules are shown in the illustratedembodiment, it should be understood that any number of modules could beused, and that individual thermoelectric elements with appropriateassociated insulation could also be employed.

The modules 14 and 16 are preferably connected in series, the output ofboth modules being coupled into a compartment 20 in a manner not shown.Compartment 20 contains various circuitry for amplifying the signal fromthe thermoelectric modules. Typically, this circuitry comprises a DC-DCvoltage conversion circuit to accept power from the thermoelectricmodules at a low voltage and produce an output at a higher voltage. Thishigher voltage output is usually delivered as a charging current tobatteries.

The apparatus in FIG. 1 also includes an air intake 22 and a hose orconduit 24 for passing air therethrough to burner unit 12. A fuel lineconnector 26 is connected to a supply of fuel, which may take the formof a suitable combustible gas such as methane, propane, butane, naturalgas, etc. stored under pressure. Fuel gas is passed through variousfittings, the pressure of the fuel gas being adjustable by means of apressure regulator 28. The temperature achieved by burner unit 12 can beregulated by means of adjustment of pressure regulator 28. The fuel gasflows through a section of restrictive tubing, shown schematically at30, and into a series of fittings 32 which are connected to burner unit12. The fuel gas is combusted within burner unit 12 in a manner whichwill be described in more detail below, thereby producing exhaust gaseswhich are passed through hose or conduit 33 so as to exit the case atexhaust outlet 34. The entire apparatus shown in FIG. 1 is preferablyoriented such that exhaust gases from exhaust outlet 34 flow in agenerally downward direction. One benefit derived from the downward flowof the exhaust is that the exhaust can be cooled well below thecondensation temperature of water at the point of release, withoutcollecting water within the apparatus. An additional preferred featureshown in FIG. 1 is a polycarbonate heat shield 36, which is shown asbroken away, mounted to case 10 so as to enclose burner unit 12. Shield36 operates at a sufficiently low temperature that it can be safelytouched when the thermoelectric generator is operating. In addition toits function as a hand guard, the shield 36 reduces convective heat lossfrom the thermoelectric generator to the interior of case 10, increasingthe power of the generator and reducing the temperature of othercomponents.

Referring now to FIG. 2, there is shown a cross sectional view of burnerunit 12. Burner unit 12 includes a shell member 38 having variouspassages therein which are hereinafter described and an interior surface40 which defines a cavity. Aluminum is the presently preferred shellmember material due to its high thermal conductivity, lightness inweight, and compatibility with many types of fuel gases. Other thermallyconductive metals or plastics could be employed, however. Shell member38 has a fuel inlet passage 42 within which one received the variousfittings denoted generally at 32. As discussed above, tubing shown inFIG. 1 is connected to fittings 32, an appropriate fuel being suppliedto inlet passage 42 accordingly. A nozzle 44 is positioned within inlet42 for receiving fuel therethrough. Preferably, an O-ring seal 46 isprovided between the interior surface of a reduced diameter end of inlet42 and nozzle 44 in order to provide an adequate seal. A spring 48 isdisposed within inlet 42 in the illustrated embodiment such that one endof the spring abuts a fitting, whereas the other end abuts nozzle 44.Therefore, a force is exerted against nozzle 44 and thus also againstO-ring 46 so as to enhance the sealing effect. Nozzle 44 has an outletorifice 49 which empties into a venturi passage 50 in shell member 38.As shown, orifice 49 is generally aligned with the longitudinal axis ofventuri passage 50, and is spaced from the upstream end of venturi 50.Venturi 50 converges from its upstream end to a throat 52, and divergesfrom throat 52 to its downstream end. An inlet passage 54 for oxidantgas is provided in shell 38 such that one end is connected to theupstream end of venturi 50. The downstream end of venturi passage 50 isconnected to another passage 56 within shell 38.

A cartridge member shown generally at 58 indisposed within the cavitydefined by interior surface 40 of shell 38. Cartridge member 58 ispreferably made of stainless steel, but other materials capable ofwithstanding high temperatures approaching 1,000° F. could also beutilized. The material used for cartridge member 58 should also berelatively corrosion resistant, and be compatible with exhaust fumesgenerated within the cartridge member. It is also preferable that thematerial used be a poor conductor of heat, the reason for which willbecome more apparent below. Cartridge 58 has an axis, a first end 59aand a second end 59b, and can be regarded as comprising a first portion60 and a second portion 62. Portion 60 axially extends from end 59a toportion 62, whereas portion 62 axially extends from portion 60 to end59b. Cartridge 58 also includes a radially extending generally annularflange 64 at end 59a. Flange 64 is preferably in contact with interiorsurface 40 around the circumference of the flange. Cartridge portion 62includes a generally annular flange 66 which is also in contact withinterior surface 40 around the circumference of the flange. Preferably,the contact between interior surface 40 of shell 38 and flanges 64 and66 as described above are the sole points of contact between cartridge58 and shell 38. Thus, a generally annular space 68 is defined betweenthe exterior surface of cartridge 58 and the interior surface of shell38. This space extends around the circumference of cartridge portion 60,and along substantially the entire length of cartridge portion 60.

Cartridge portion 60 is hollow as shown, and has an interior surface 70.Two screens, preferably made of stainless steel, are mounted withincartridge portion 60 so as to axially spaced from one another. Screen 71and 72 may be perforated plates or of any other similar structure whichwill be gas permeable. Interior surface 70 and also screen 71 and 72define a combustion chamber 74 which contains a loose bed of catalystpellets shown schematically at 76. The presently preferred catalyst is aplatinum/sodium catalyst supported on an alumina substrate. Othercatalysts, such as palladium catalysts, could also be employed as longas they are suitable for the catalytic oxidation of a fuel. For thepurpose of initiating the combustion reaction, a suitable ignitiondevice such as a DC cartridge heater 78 is inserted into the center ofthe catalyst bed.

Cartridge portion 62 includes an interior surface which defines agenerally frustoconical passage 80. Cartridge portion 62 also has aplurality of passages 82, only two of which are shown in the crosssectional view of FIG. 2. One end of each passage is connected to thesmall end of frustoconical passage 80 so as to be in fluid communicationwith chamber 74. The other end of each passage 82 is in fluidcommunication with points beyond the burner unit 12. Additionally,flange 66 and the interior surface of shell 38 are threaded as shown sothat cartridge 58 can be easily removed for maintenance, replacement ofcatalyst, etc. Finally in connection with FIG. 2, several holes such asshown at 84 are provided in shell 38 for receiving mounting poststherethrough.

Referring now to FIG. 3, an end view of burner unit 12 shows passages 82and cartridge portion 62. The mounting arrangement of one thermoelectricmodule 16 is also illustrated. The thermoelectric module used in theillustrated embodiment comprises two insulating plates 86 and 88 betweenwhich are sandwiched a plurality of thermoelectric elements such asshown schematically at 90. Plate 86 is in direct contact with theexterior surface of shell 38, and plate 88 is in direct contact withcase 10. Plate 86 forms the hot side of module 16, whereas plate 88forms the cold side. Thermoelectric elements 90 are in direct thermalcontact with the exterior surface of shell 38 such that substantially noair spaces exist between the exterior surface of shell 38 and thethermoelectric elements. Although case 10 is conveniently used in theillustrated embodiment as a heat sink, it should be understood that anyother suitable heat sink could be employed such as heat dissipatingfins, for example. Most preferably, a thermally conductive plastic or aconductive grease such as silicon grease loaded with thermallyconductive particles is interposed between each of plates 86 and 88 andits respective surface which it contacts.

The apparatus shown in FIGS. 2 and 3 operates as follows. A suitablefuel gas such as propane, butane, natural gas, etc. is passed into inlet42. The gas then flows through nozzle 44 so as to exit the nozzle fromorifice 49. The apparatus uses the jet pump principle to ingest airthrough inlet 54, wherein momentum is transferred from the gas jet toair which has entered inlet 54. The air flow rate is determined by therate that momentum is imparted to the air/fuel mixture by the gas jetleaving the orifice. The rate of momentum transfer is identical to therecoil thrust produced by a gas jet. It can be shown that to a goodapproximation, the rate of momentum transfer, and thus the air flowrate, is constant for all fuel gas compositions.

Fuel gas and air ingested as described above mix together to form amixture which is pumped through venturi passage 50 and then throughpassage 56 so as to be introduced to combustion chamber 74. Preferablythe mixture introduced to combustion zone 74 is very fuel rich. Mostpreferably, the air/fuel volume flow ratio is less than thestoichiometric ratio for methane, which is about 9.54. As used herein,the stoichiometric ratio for a particular fuel gas is that air/fuelratio at which there is theoretically sufficient oxygen to completelyconsume the fuel gas. Fuels of higher heating value than methane requirea greater volume of air than required by methane for complete combustionof a particular volume of fuel. Since methane is about the lowestheating value fuel, employing other fuels having a higher heating valuewill produce approximately the same quantity of heat as methane ifcombustion is air-limited as described above. Therefore, combustion isconstrained by the air available, and the power produced andtemperatures achieved are not a strong function of the composition ofthe fuel gas. By providing an air/fuel ratio below the stoichiometricratio for methane one may conveniently change from one fuel gas toanother fuel gas while maintaining a relatively constant power outputwithout making any adjustments in the apparatus. One disadvantage isthat such a highly fuel rich mixture causes a large fraction of the fuelto be left unburned, and thus a loss of combustion efficiency. However,the cost of fuel is not an important consideration due to the very lowflow rate device shown in FIGS. 2 and 3. Some other advantages of thefuel rich mixture include a greater driving pressure through thecatalyst bed than would be achieved with a greater volume of air, andeasier ignition than in the case where more air is present.

The fuel rich mixture as described above is achieved by carefullysetting certain parameters. Such parameters which effect the air/fuelratio include size of the nozzle outlet orifice 49, gas pressure at theorifice, size of the venturi passage 50, particularly in the throatportion 52 and back pressure resulting from the catalyst bed. Probablythe most important parameter is the size of venturi passage 50. Bychanging the size of the venturi passage, the air flow rate can bechanged, whereas the fuel gas flow rate remains unchanged. The size ofventuri passage 50 establishes the area available for the expanding jetof gas to mix with the air. Generally speaking, as the size of venturipassage 50 is decreased, the flow rate of air ingested by the jetprinciple as previously described is also decreased.

The combustible mixture passes through screen 71 and into combustionchamber 74 which contains catalyst pellets. Ignitor 78 is activated fora predetermined period of time, usually several minutes, to initiate thecommbustion reaction. Flameless catalytic oxidation of the fuel gastakes place within combustion chamber 74 accordingly, thereby generatingheat. Typically, temperatures from about 800° F. to about 1000° F. areachieved within the combustion chamber. Combustion product gases passfrom combustion chamber 74 through frustoconical passage 80, and throuhpassages 82 so as to be exhausted from burner unit 12. Surfaces whichdefine passages 82 serve as a heat exchange surface area within thecartridge. Heat is effectively scavenged from the exhaust gases in thisheat exchange area. This enhances the ability of the burner unit tooperate over a broad temperature range as at high ambient temperaturesthe exhaust gases pass through the heat exchange area at too high atemperature for condensation of the water produced by combustion. Thisreduces the power produced within the burner. At low ambienttemperatures, however, the moisture is condensed within this region anda greater fraction of the heat of combustion is delivered to the burner.Heat generated within the combustion chamber is transferred fromcartridge member 58 to shell member 38 by convective and radiant heatexchange across space 68. Heat is also transferred to shell member 38 atthe point of contact between flanges 64 and 66 with the interior surfaceof shell 38. Heat transferred as described above is received by the hotsides of the thermoelectric modules in contact with the exterior surfaceof shell member 38. Case 10, which serves as a heat sink, maintains thecold sides of the modules at a relatively low temperature, thusestablishing the required temperature difference across the modules.This temperature difference or gradient causes the thermoelectricelements in each module to generate electrical energy.

As discussed above, problems can potentially arise where a fuel gas isused which has a high concentration of hydrogen sulfide. If thetemperature within the combustion chamber is maintained at too low alevel the hydrogren sulfide within the fuel gas will break down toelemental sulfur and coat the catalyst pellets within the chamber. Suchcoating of the pellets can render the catalyst inactive. The mountingarrangement of cartridge member 58 within shell 38 provides asignificant degree of thermal resistance between combustion chamber 74and shell 38. Therefore, the temperature within combustion chamber 74can be maintained at a much higher temperature than the exterior surfaceof shell 38 (which also corresponds to the temperature of the hot sideof the thermoelectric modules). Low cost thermoelectric modules such asthose used in the illustrated embodiment typically have a maximumoperating temperature of about 300° F., above which various solderconnections in the module will start to melt. In a burner unitconstructed according to the present invention, the hot sides of thethermoelectric sides of the modules can be maintained below theirmaximum operating temperatures, while at the same time the temperaturewithin the combustion chamber can be maintained at a relatively highlevel of about 800° F. to about 1000° F. At such combustion chambertemperatures, oxidation of sulfur in hydrogen sulfide produces suchproducts as SO₂ and H₂ SO₄ which pass out of the burner unit with otherexhaust gases. Thus, substantially no elemental sulfur is produced whenthe combustion chamber operates at the above cited temperatures, suchthat plating of the catalyst is thereby avoided.

Certain other additional advantages reside in the apparatus of thepresent invention. One additional advantage is that the burnertemperature is self regulated to a great extent. This is due to theenbloc construction of the nozzle and venturi into the same body, theshell, which receives heat from the combustion chamber. Generallyspeaking, the rate that momentum is delivered to the air/fuel mixturewill decrease with increasing temperature. Thus, as the shell 38increases in temperature, venturi 50 and nozzle 44 increase intemperature. Because of the decreased momentum delivered to the air/fuelmixture, the amount of gas and air pumped into the combustion chamber isreduced, and the operating temperature of the combustion chamber is alsoreduced. Thus, this construction provides for a degree of selfregulation of the burner temperature. In addition, certain features ofthe thermoelectric generator described above allow its applicationwithout posing an ignition hazard for combustible gas vapors. Forexample, temperatures are maintained well below 390° F. on exposedsurfaces. These temperatures are well below the ignition temperatures ofmost vapors which might come into contact with such hot exposedsurfaces. The ignition hazard is also minimized due to the oxygendepleted nature of exhaust gases. The exhaust gases are typically fartoo depleted to support combustion. Even when the exhaust gases aremixed with air, ignition of the exhaust gases is precluded by thecooling effect of the heat exchange area in the cartridge. The exhaustgases are cooled in the heat exchange area well below their ignitiontemperature. Ignition of the air/fuel mixture before reaching thecombustion chamber is also unlikely due to the fact that the temperatureof all metal surfaces in passages leading to the combustion chamberremain below the ignition temperature of the air/fuel mixture. Ignitionof combustible vapors due to flash back is also precluded by the veryrich mixture employed.

A concrete example will now be described which should not be construedto limit the invention in any manner. A thermoelectric generatorsubstantially similar to that shown in FIGS. 1-3 was constructed andtested. The cartridge was constructed of stainless steel, and the shellwas constructed of aluminum. The catalyst employed was 0.5% platinumwith 0.4% sodium on 1/8 inch diameter by 1/8 inch long tablets. A 36gram charge of the catalyst tablets was supported within the cartridge.A 12 volt, 5 amp DC cartridge heater was utilized to initiate thecombustion reaction. Certain important dimensions include a venturithroat diameter of 0.141 inch, and a nozzle orifice diameter of 0.010inch. With respect to certain operating conditions, the pressure at theorifice was set at 1 psig and the flow rates for fuel gas and air wereabout 0.72 scfh and about 4.6 scfh respectively, giving an air/fuelratio of about 6.4.

The apparatus described above was first operated using methane as thefuel gas. The apparatus was operated in a temperature chamber in anambient temperature of 130° F. for about 3 hours. Referring to FIG. 4,curve 92 is a plot of ambient temperature versus time, wherein the timescale begins at 8.85 hours. The curve 94 is a plot of the burner unittemperature at a point on the shell near the thermoelectric modules. Itcan be seen from this curve that the thermoelectric modules remain wellbelow 300° F., which is their approximate maximum operating temperature.The output in volts of the thermoelectric generator is plotted versustime, the curve so obtained being shown at 96. A relatively constantelectrical power output in excess of 1 watt is reliably obtained.

The thermoelectric generator constructed according to the presentexample was also tested using sour gas containing hydrogen sulfide (H₂S). Referring to FIG. 5, power output is plotted versus time for thegenerator starting up on a mixture of 9.9% H₂ S in methane. Subsequentfield testing demonstrated the ability of the generator to start and runfor a month on a gas containing about 20% H₂ S. At the end of about amonth, there was some clogging of the exhaust hose, the generator wasrestarted and operated with a normal power output. The generator wasalso operated for three months on gas containing about 8% H₂ S. At theend of the three months, the generator still operated normally,indicating no apparent degradation of the catalyst.

The ability of the generator to operate on a wide variety of fuels wasinvestigated by operating on methane, methane blended with nitrogen toobtain lower BTU values, methane blended with propane to obtain higherBTU values, and even on pure propane. The lowest heating value on whichthe generator would operate was about 700 BTU/CF. At the other end ofthe scale, it was found that as the heat value rose past 1400 BTU/CF,the power output ceased to increase with heat value. Referring to FIG.6, the curve shown at 98 illustrates the output initially running onmethane, propane being introduced for a step change from about 1000BTU/CF to more than 2500 BTU/CF, with an apparent power increase of onlyabout 25%. This confirms that the power is more constrained by the airavailable than by the fuel heat value. Also in FIG. 4, curve 100 is aplot of shell temperature (near the modules) versus time, and the curveshown at 102 is a plot of ambient temperature versus time.

Obviously many modifications and variations of the present invention arepossible in light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is:
 1. A thermoelectric generator comprising:a hollowmember which defines a combustion chamber therein, wherein said chambercontains a catalyst; a means capable of introducing into said chamber amixture of a combustible fuel and air having an air/fuel ratio less thanthe stoichiometric ratio for methane; at least one thermoelectricelement positioned to receive heat generated in said chamber.
 2. Amethod of thermoelectric power generation comprising:flowing a mixtureof combustible fuel and air through a catalyst which is contained in acombustion chamber the air/fuel ratio of the mixture being less than thestoichiometric ratio for methane; combusting the fuel, by catalyticoxidation thereof, in the chamber to produce heat; providing the heat toat least one thermoelectric element.
 3. A method as recited in claim 2,wherein said air/fuel ratio is about 6.4.